This invention relates to target passive ranging and, more particularly, to determining passively the range from ownship to a target from estimates of predetermined initial target conditions or parameters without need to make a maneuver by ownship. The range determination is based on actual measurements of predetermined parameters of the target, other than range to target.
An estimate of range to, and/or velocity of, an object or target, especially from an airborne ownship in a potentially hostile environment, may be desired. Further, although active ranging, such as by use of a radar system that transmits electromagnetic energy and then receives a portion of the energy that is reflected from a target for generating such parameters of the target may be available, it may be desirable to determine target parameters passively, such as by use of an infrared (IR) signature of the target, so that ownship presence and location are not unduly and unnecessarily compromised.
A presently employed ranging technique computes range to an airborne target from a second airborne craft, or ownship, by performing ownship maneuvers in such a way as to obtain angular information (elevation and azimuth with respect to ownship) for "triangulating" on the target to estimate range to target. A single Kalman filter is generally used in the triangulation approach. Problems associated with this approach are that ownship is required to make maneuvers and that the resulting accuracy is a direct function of these ownship maneuvers for a given angle measurement accuracy and true range to the target. Further, such maneuvering may take about one minute, or at least tens of seconds for fighter-like aircraft, in order to achieve the desired accuracy, and maneuvering significantly increases the probability of detection by a hostile target having detection capabilities.
It would be desirable to provide a system capable of producing estimates of range to a target from ownship within a predetermined accuracy, without having to make any ownship maneuvers. That is, to obtain such estimates while ownship maintains a constant course, or heading, and velocity. For purposes herein, ownship maneuvers may be considered to be events, such as turning, accelerating, decelerating, changing altitude, etc., which deviate from a constant heading, altitude and velocity.